Monkeys And Humans Use Parallel Mechanism To Recognize Faces

July 12, 2009— Researchers at the Yerkes
National Primate Research Center, Emory University, have demonstrated
for the first time rhesus monkeys and humans share a specific
perceptual mechanism, configural perception, for discriminating among
the numerous faces they encounter daily. The study, reported in the
June 25 online issue of Current Biology, provides insight into the
evolution of the critical human social skill of facial recognition,
which enables us to form relationships and interact appropriately with
others.

"Humans and other social primates need to recognize other
individuals and to discriminate kin from non-kin, friend from foe and
allies from antagonists," said lead researcher Robert R. Hampton of the
Yerkes National Primate Research Center and Emory's Department of
Psychology. "Our research indicates the ability to perform this skill
probably evolved some 30 million or more years ago in an ancestor
humans share with rhesus monkeys."

The remarkable capability humans have to distinguish among thousands
of faces stems from our sensitivity to the unique configuration, or
layout, of facial features. "Because faces share so many features in
common – eyes, nose, mouth, etc. – the simple detection of the
collection of these features alone would not permit us to tell many
faces apart," Dr. Hampton noted. "It's our ability to perceive small
changes in the relations among the features that enables us to
distinguish thousands of faces and recognize those we know," he
explained.

Hampton and his research team used the Thatcher Effect, a perceptual
illusion named for Margaret Thatcher because it was first demonstrated
using an image of the former British prime minister, to determine if
rhesus monkeys use configural perception to recognize other monkeys. In
the study, the researchers presented images of six different monkeys to
four 4-year-old rhesus macaque monkeys raised for two to three years in
large social groups at the Yerkes Research Center.

The researchers "thatcherized" the images of faces by positioning
the eyes and mouths upside down relative to the rest of each face. The
researchers presented monkeys with normal images of each face upside
down and right side up until the monkeys were bored and ceased looking
at the pictures. The researchers then showed the monkeys the
thatcherized faces. In the upright position, the monkeys were surprised
by the distorted features and began looking at the pictures again. In
contrast, when the faces were upside down, they were not at all
surprised and treated the faces as if nothing had been done to them.

This is similar to the human response to the Thatcher Effect, which
shows that when the eyes and mouth are rotated and, thus, distorted,
humans surprisingly process the upside-down version of the image more
as a collection of features and with less emphasis on the relations
among the features. As a result, the face appears fairly normal despite
being thatcherized. However, when viewed right side up, humans say the
image looks awkward or grotesque, demonstrating they clearly see the
eyes and mouth have been rotated.

"This study advances our understanding of social processes critical
for a healthy and successful social life in primates. Early primates
apparently solved the problem of recognizing each others' faces in this
way well before humans arrived on the planet," Dr. Hampton concluded.

For nearly eight decades, the Yerkes National Primate Research
Center, Emory University, has been dedicated to conducting essential
basic science and translational research to advance scientific
understanding and improve the health and well-being of humans and
nonhuman primates. Today, the center, as one of only eight National
Institutes of Health-funded national primate research centers, provides
leadership, training and resources to foster scientific creativity,
collaboration and discoveries. Yerkes-based research is grounded in
scientific integrity, expert knowledge, respect for colleagues, and
open exchange of ideas and compassionate quality animal care.

Within the fields of microbiology and immunology, neuroscience,
psychobiology and sensory-motor systems, the center's research programs
are seeking ways to: develop vaccines for infectious and noninfectious
diseases, such as AIDS and Alzheimer's disease; treat cocaine
addiction; interpret brain activity through imaging; increase
understanding of progressive illnesses such as Parkinson's and
Alzheimer's; unlock the secrets of memory; determine behavioral effects
of hormone replacement therapy; address vision disorders; and advance
knowledge about the evolutionary links between biology and behavior.